Spontaneously formed clear silicone microemulsions

ABSTRACT

A method of spontaneously forming a highly stable clear microemulsion by combining (i) water; (ii) a volatile cyclic methyl siloxane or volatile linear methyl siloxane; and (iii) a silicone polyether surfactant. The amounts of each component are such that the composition is in the form of a microemulsion. The volatile methyl siloxane is present in the microemulsion in the form of particles having an average diameter of less than about 100 nanometers. The microemulsion is useful in personal care products.

BACKGROUND OF THE INVENTION

This invention is directed to an optically clear silicone microemulsionformed with very little input of mechanical energy for mixing thecomponents. More particularly, a ternary composition of water, avolatile cyclic or linear methyl siloxane (VMS), and a short-chain orlow molecular weight silicone polyether, spontaneously providesoptically clear microemulsions when combined with only hand agitation.

It is well documented (U.S. Pat. No. 4,999,398) that emulsions,especially silicone emulsions, are opaque, cloudy, and tend to separateon standing. Thus, the desirability of microemulsions, which containmicro-particles in the droplet phase, providing a measure of clarity.

As used herein, the term emulsion or macroemulsion means a dispersion ofone immiscible liquid in another, in the form of droplets, withdiameters approximately in the range of 100-1,000 nanometers (0.1-1.0microns/1,000-10,000 angstroms Å). In contrast, a microemulsion means atransparent, thermodynamically stable, dispersion of two or moreimmiscible liquids and a surfactant.

Microemulsions are clear or transparent because they contain particlessmaller than the wavelength of visible light, which is typically onorder of about 10-100 nanometers. Microemulsions may contain oildroplets dispersed in water (O/W), water droplets dispersed in oil(W/O), or they may be in the form of a bicontinuous structure. They arecharacterized by an ultra-low interfacial tension between the oil andwater phases.

A microemulsion can be recognized by several of its inherentcharacteristics which are that (i) it contains oil, water, and asurfactant; (ii) there is a high concentration of surfactant relative tooil; (iii) the system is optically clear; (iv) the phases do notseparate by centrifugation; and (v) the system forms spontaneously.

Thus, for purposes of my invention, an emulsion is considered ascontaining particles having an average diameter of more than 100nanometers (0.1 microns/1,000 angstroms Å), whereas a microemulsioncontains particles having an average diameter of less than 100nanometers (0.1 microns/1,000 angstroms Å). Clarity or transparency iscontrolled to a great extent by the particle size of the dispersedphase. The scattering of light is dependent on the particle size.Therefore, clear or transparent compositions appear to be a single phasewithout droplets or particles when viewed with the naked eye, as definedhereafter.

While Bailey in U.S. Pat. No. 3,299,112 describes emulsions formed fromwater, a silicone oil, and a silicone polyether, Bailey's emulsions arenot clear; and require input of substantial mechanical energy toprepare. Furthermore, in contrast to my invention, the ternary system inthe '112 patent is not a microemulsion; the silicone oil is not avolatile cyclic VMS; and where Bailey does describe a linear siliconeoil, it is not a volatile linear silicone. Thus, the silicone oil inBailey corresponds to R"₃ SiO(R"₂ SiO)_(x) SiR"₃ where x is 10-1,000. Mycorresponding volatile linear VMS have an "x" of 0-5, well below therange in Bailey. In fact, I discovered that where "x" exceeds 5, theemulsions tend not to be clear.

In addition, emulsions are recognized as inherently unstable systemsseparating with time. In contrast, my microemulsions form spontaneouslyand are stable indefinitely. The order of addition of the componentsdoes not influence their formation, and simple hand shaking in thetemperature range of their stability is sufficient to cause themicroemulsions to form.

My spontaneously formed clear microemulsions have particular value inthe personal care arena. Because of the unique volatilitycharacteristics of the VMS component of my ternary system, it can beused alone, or blended with other cosmetic fluids, to form a variety ofover-the-counter personal care products.

Thus, it is useful as a carrier in antiperspirants and deodorants, sinceit leaves a dry feel, and does not cool the skin upon evaporation. It islubricious and will improve the properties of skin creams, skin carelotions, moisturizers, facial treatments such as acne or wrinkleremovers, personal and facial cleansers, bath oils, perfumes, colognes,sachets, sunscreens, pre-shave and after-shave lotions, shaving soaps,and shaving lathers. It can be used in hair shampoos, hair conditioners,hair sprays, mousses, permanents, depilatories, and cuticle coats, toenhance gloss and drying time, and provide conditioning benefits. Incosmetics, it will function as a leveling and spreading agent forpigments in make-ups, color cosmetics, foundations, blushes, lipsticks,eyeliners, mascaras, oil removers, color cosmetic removers, and powders.It is useful as a delivery system for oil and water soluble substancessuch as vitamins. When incorporated into sticks, gels, lotions,aerosols, and roll-ons, my ternary composition imparts a dry,silky-smooth, payout.

In addition, because my spontaneously formed clear microemulsionsexhibit a variety of advantageous and beneficial properties such as (i)clarity, (ii) very small particle size, (iii) ultra-low interfacialtensions, (iv) the ability to combine properties of water and oil in asingle homogeneous fluid, (v) shelf stability, and (vi) ease ofpreparation; they have wide application, but especially inantiperspirants, deodorants, in perfumes as a carrier, and hairconditioning.

BRIEF SUMMARY OF THE INVENTION

It is an object of my invention to form a clear microemulsion by simplycombining (i) water; (ii) a volatile cyclic methyl siloxane or volatilelinear methyl siloxane; and (iii) a silicone polyether.

What I have accomplished is significant, because I discovered how tomake clear products without involving the use of high shear, heretoforerequired to obtain the small particle size necessary to achieve clarity.

These clear microemulsions form spontaneously in the sense that they donot require energy input by means of mixing and shear devices. Thus,turbines, impellers, colloid mills, homogenizers, or sonolators, are notrequired to form these systems. It is only necessary that theappropriate amounts of the three components be added to a suitablecontainer, and the container hand shaken. Of course, the components canbe mixed or sheared with more energy input, and the microemulsions willstill be obtained, but no advantage results from such additional energyusage.

These and other objects of my invention will become apparent from aconsideration of the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a ternary phase diagram of the system comprising water,octamethylcyclotetrasiloxane (D₄), and the silicone surfactant, fordetermining composition ranges of microemulsions prepared according toExample XIII of my invention. The compositions are defined by the shadedarea depicted in FIGURE 1.

In FIGURE 1, each of the corners represents 100 percent of the componentlabelled there. The side of the triangle directly opposite each cornerrepresents zero percent of that component. Lines parallel to theopposite side represent increasing amounts of that component as theybecome closer to the corner. Any line drawn from the corner of ComponentA to the opposite side represents varying the amount of Component A at aconstant ratio of the other two components.

The composition of any point within the shaded area is determined bydrawing lines parallel to each of the three sides through the point. Theamount of each component is then read from the intersection of each linewith the side of the triangle which corresponds to that component, i.e.the side beginning at 100 at each component's corner.

DETAILED DESCRIPTION

My ternary composition contains water, a volatile cyclic or linearmethyl siloxane (VMS), and a short-chain or low molecular weightsilicone polyether. Those three components can be combined to form clearcompositions without the addition of other materials.

Thus, the composition should be free of non-essential ingredients suchas salts; co-surfactants; monohydroxy alcohols; and diols and triolssuch as ethylene glycol and glycerol. The elimination of suchnon-essential ingredients is especially beneficial and advantageous, asit obviates the need for refractive index matching, often resorted to inthe past to achieve clear or transparent products.

The three components can be combined in any given order of addition.While heat enhances solubility, lowers surface tension, and reducesviscosity, its application is not required. Room temperature (20°-25°C./68°-77° F.) is sufficient in most cases.

The oil component of my ternary composition is a volatile methylsiloxane (VMS), which is a low viscosity silicone fluid corresponding tothe average unit formula (CH₃)_(a) SiO.sub.(4-a)/2 in which a has anaverage value of two or three. The fluid contains siloxane units joinedby .tbd.Si--O--Si.tbd. bonds. Representative units are monofunctional"M" units (CH₃)₃ SiO_(1/2) and difunctional "D" units (CH₃)₂ SiO_(2/2).The presence of trifunctional "T" units CH₃ SiO_(3/2) results in theformation of branched cyclic volatile methyl siloxanes. The presence oftetrafunctional "Q" units SiO_(4/2) results in the formation of branchedlinear volatile methyl siloxanes.

Linear VMS have the formula (CH₃)₃ SiO{(CH₃)₂ SiO}_(x) Si(CH₃)₃, andcyclic VMS have the formula {(CH₃)₂ SiO}_(y), in which x is 0-5, and yis 3-6. Preferably, the volatile methyl siloxane has a boiling pointless than 250° C. and a viscosity of 0.65-5.0 centistokes (mm² /s).

Some representative volatile methyl siloxanes are: ##STR1##

The cyclic volatile methyl siloxanes (II) have been assigned theInternational Nomenclature Cosmetic Ingredient (INCI) name"CYCLOMETHICONE" by The Cosmetics, Toiletries and Fragrance Association,Inc., (CTFA) Washington, D.C. Cyclic and linear methyl siloxanes areclear fluids, essentially odorless, non-toxic, non-greasy, non-stinging,and non-irritating to skin. VMS leave substantially no residue afterthirty minutes at room temperature (20°-25° C./68°-77° F.) when one gramis placed at the center of No. 1 circular filter paper of 185millimeters diameter, supported at its perimeter in open roomatmosphere. Volatile methyl siloxanes may be used alone or mixedtogether. Mixtures result in solutions having evaporating behaviorsdifferent from individual fluids.

Representative linear volatile methyl siloxanes (I) arehexamethyldisiloxane (MM) with a boiling point of 100° C., viscosity of0.65 mm² /s, and formula Me₃ SiOSiMe₃ ; octamethyltrisiloxane (MDM) witha boiling point of 152° C., viscosity of 1.04 mm² /s, and formula Me₃SiOMe₂ SiOSiMe₃ ; decamethyltetrasiloxane (MD₂ M) with a boiling pointof 194° C., viscosity of 1.53 mm² /s, and formula Me₃ SiO(Me₂ SiO)₂SiMe₃ ; dodecamethylpentasiloxane (MD₃ M) with a boiling point of 229°C., viscosity of 2.06 mm² /s, and formula Me₃ SiO(Me₂ SiO)₃ SiMe₃ ;tetradecamethylhexasiloxane (MD₄ M) with a boiling point of 245° C.,viscosity of 2.63 mm² /s, and formula Me₃ SiO(Me₂ SiO)₄ SiMe₃ ; andhexadecamethylheptasiloxane (MD₅ M) with a boiling point of 270° C.,viscosity of 3.24 mm² /s, and formula Me₃ SiO(Me₂ SiO)₅ SiMe₃.

Representative cyclic volatile methyl siloxanes (II) arehexamethylcyclotrisiloxane (D₃) a solid with a boiling point of 134° C.and formula {(Me₂)SiO}₃ ; octamethylcyclotetrasiloxane (D₄) with aboiling point of 176° C., viscosity of 2.3 mm² /s, and formula{(Me₂)SiO}₄ ; decamethylcyclopentasiloxane (D₅) with a boiling point of210° C., viscosity of 3.87 mm² /s, and formula {(Me₂)SiO}₅ ; anddodecamethylcyclohexasiloxane (D₆) with a boiling point of 245° C.,viscosity of 6.62 mm² /s, and formula {(Me₂)SiO}₆.

Representative branched volatile methyl siloxanes (III) and (IV) areheptamethyl-3-{(trimethylsilyl)oxy}trisiloxane (M₃ T) with a boilingpoint of 192° C., viscosity of 1.57 mm² /s, and formula C₁₀ H₃₀ O₃ Si₄ ;hexamethyl-3,3,bis {(trimethylsilyl)oxy} trisiloxane (M₄ Q) with aboiling point of 222° C., viscosity of 2.86 mm² /s, and formula C₁₂ H₃₆O₄ Si₅ ; and pentamethyl {(trimethylsilyl)oxy} cyclotrisiloxane (MD₃)with the formula C₈ H₂₄ O₄ Si₄.

One preferred VMS component of my ternary system isoctamethylcyclotetrasiloxane (CH₃)₂ SiO!₄. It has a viscosity of 2.3centistokes (mm² /s) at 25° C., and is referred to as "D₄ " since itcontains four difunctional "D" units (CH₃)₂ SiO_(2/2) shown as: ##STR2##

Four "D" units combine to form octamethylcyclotetrasiloxane shown ineither formula below: ##STR3##

In the literature, D₄ is often called CYCLOMETHICONE or TETRAMER. It hasa higher viscosity (2.3 cs) and is thicker than water (1.0 cs), yetoctamethylcyclotetrasiloxane needs 94% less heat to evaporate thanwater.

Another preferred VMS component of my ternary system isdecamethylcyclopentasiloxane (D5) often referred to as PENTAMER. It isshown structurally below: ##STR4##

A benefit offered by using VMS compounds is that many local, state,federal, and international regulations, have restricted the use ofcertain chemicals, but VMS is a suitable replacement. Thus, theEnvironmental Protection Agency (EPA) determined that volatile methylsiloxanes such as octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,hexamethyldisiloxane, octamethyltrisiloxane, anddecamethyltetrasiloxane, were acceptable substitutes for the CFC-113chlorofluorocarbon (C₂ Cl₃ F₃) and methylchloroform (MCF). Thisdetermination is limited to cleaning in closed systems, for metalcleaning, electronic cleaning, and precision cleaning applications,under the EPA's Significant New Alternatives Policy (SNAP).

In addition, the EPA excluded VMS as a volatile organic compound (VOC).Thus, they added VMS to a list of compounds in 40 CFR 51,100(s) excludedfrom the definition of VOC, on the basis that VMS compounds havenegligible contribution to tropospheric ozone formation. They pointedout that exempting VMS from regulation as an ozone precursor contributesto achievement of several important environmental goals, in that VMSmight be used as a substitute for compounds listed as hazardous airpollutants (HAP). As they explained, that met the need to developsubstitutes for ozone depleting substances (ODS), and attained NationalAmbient Air Quality Standards for ozone under Title I of the Clean AirAct.

The other component of my ternary system, in addition to water and VMS,is a short-chain or low molecular weight silicone polyether.Representative polyether structures are: ##STR5##

A cyclic polyether of the type shown below can also be used. ##STR6##

In these structures, R1 represents an alkyl group containing 1-6 carbonatoms such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; R2represents the radical --(CH₂)_(a) O(C₂ H₄ O)_(b) (C₃ H₆ O)_(c) R3; xhas a value of 0-3; y has a value of 1-3; z has a value of 0-2; m has avalue of 3-5; n is one; a has a value of 3-6; b has a value of 4-20; chas a value of 0-5; and R3 is hydrogen, a methyl radical, or an acylradical such as acetyl. Preferably, R1 is methyl; b is 6-12; c is zero;and R3 is hydrogen.

Compositions according to my invention may contain 5-70% by weight ofsurfactant, but most preferably, they contain about 15-30% by weight ofthe surfactant. The balance of the composition is oil and water, withthe proportions of oil and water generally falling between 40:60 to80:20, or 0.4 to 0.8 as defined below for Ratio 1.

For purposes of my invention, the criteria used to determine opticalclarity is whether text can be read with the naked eye through a twocentimeter diameter bottle filled with the microemulsion.

As noted in the textbook Microemulsions Theory and Practice, Edited byLeon M. Prince, Academic Press, Inc., Pages 7-10, New York (1977), the"Visual recognition of microemulsions should not be taken lightly. Infact, the microemulsion chemist should train himself carefully in thisart. Use of sunlight rather than an artificial source of light isrecommended. The eye is better than a microscope because the limit ofresolution of a light microscope in blue light is only about 0.1 μm sothat droplets smaller than 0.14 μm cannot be seen".

The following examples show my invention in more detail.

EXAMPLE I

I formed optically clear microemulsions spontaneously at temperaturesranging between 47°-62° C. by merely adding to a container, 50 parts ofde-ionized water, 50 parts of octamethylcyclotetrasiloxane (D4), and 25parts of silicone polyether. No mixing, stirring, shearing, or input ofmechanical energy for agitating the three ingredients was required. Thepolyether corresponded to the compound: ##STR7## where R1 was methyl, xwas zero, y was one, and R2 was --(CH₂)₃ (OC₂ H₄)₈ OH. I was able toread text through a two centimeter diameter bottle filled with themicroemulsions. I determined that the microemulsions contained particleshaving an average diameter of less than 100 nanometers (0.1 microns).

EXAMPLE II

I repeated Example I and formed clear microemulsions spontaneously attemperatures ranging between 60°-68° C. by merely combining in acontainer, 50 parts of de-ionized water, 50 parts ofdecamethylcyclopentasiloxane (D5), and 25 parts of silicone polyether.The optical clarity was the same as obtained in Example I.

EXAMPLE III

I repeated Example I and formed clear microemulsions spontaneously attemperatures ranging between 44°-60° C. by merely combining in acontainer, 60 parts of de-ionized water, 40 parts ofoctamethylcyclotetrasiloxane (D4), and 17.65 parts of siliconepolyether. The optical clarity was the same as obtained in Example I.

EXAMPLE IV

I repeated Example III including the use of salt which is anon-essential ingredient. I formed clear microemulsions spontaneously attemperatures ranging between 20°-30° C. by merely combining in acontainer, 50 parts of an aqueous solution containing 15% sodiumchloride, 50 parts of octamethylcyclotetrasiloxane (D4), and 17.65 partsof silicone polyether. The optical clarity was the same as obtained inExample III.

EXAMPLE V

I repeated Example IV and formed clear microemulsions spontaneously attemperatures ranging between 22°-41° C. by merely combining in acontainer, 30 parts of an aqueous solution containing 15% sodiumchloride, 70 parts of octamethylcyclotetrasiloxane (D4), and 25 parts ofsilicone polyether. The optical clarity was the same as obtained inExample IV.

EXAMPLE VI

I repeated Example II and formed clear microemulsions spontaneously attemperatures ranging between 30°-85° C. by merely combining in acontainer, 50 parts of de-ionized water, 50 parts ofdecamethylcyclopentasiloxane (D5), and 66.67 parts of siliconepolyether. The optical clarity was the same as obtained in Example II.

The following four examples illustrate preparation of clearantiperspirants. In Examples VII-X, an antiperspirant active wasincorporated into my clear silicone microemulsion without input ofmechanical energy for mixing the components.

EXAMPLE VII

I repeated Example I and formed clear microemulsions spontaneously attemperatures ranging between 42°-58° C. by merely combining in acontainer, 50 parts of an aqueous solution containing 25% of theantiperspirant active Aluminum Chlorohydrate (ACH-303), 50 parts ofoctamethylcyclotetrasiloxane (D4), and 25 parts of silicone polyether.The optical clarity was the same as obtained in Example I.

EXAMPLE VIII

I repeated Example VII and formed clear microemulsions spontaneously attemperatures ranging between 36°-69.6° C. by merely combining in acontainer, 50 parts of an aqueous solution containing 25% of theantiperspirant active Aluminum-Zirconium Tetrachlorohydrex-Gly(ACH-370), 50 parts of octamethylcyclotetrasiloxane (D4), and 28.2 partsof silicone polyether. The optical clarity was the same as obtained inExample VII.

EXAMPLE IX

I repeated Example VII and formed clear microemulsions spontaneously attemperatures ranging between 30°-46° C. by merely combining in acontainer, 50 parts of an aqueous solution containing 50% of theantiperspirant active Aluminum Chlorohydrate (ACH-303), 50 parts ofoctamethylcyclotetrasiloxane (D4), and 21.95 parts of siliconepolyether. The optical clarity was the same as obtained in Example VII.

EXAMPLE X

I repeated Example VII and formed clear microemulsions spontaneously atroom temperature by merely combining in a container, 63 parts of anaqueous solution containing 25% of the antiperspirant active AluminumChlorohydrate (ACH-303) and 15% of sodium chloride, 37 parts ofoctamethylcyclotetrasiloxane (D4), and 20.5 parts of silicone polyether.The optical clarity was the same as obtained in Example VII.

Other antiperspirant actives such as Aluminum Sesquichlorohydrate saltscan be used in Examples VII-X. Suitable antiperspirants products can beformulated containing a maximum use level of antiperspirant active of20% by weight AZG and 25% by weight ACH, on an anhydrous basis.

The following examples illustrate preparation of compositions accordingto my invention using a linear volatile methyl siloxane instead of acyclic volatile methyl siloxane.

EXAMPLE XI

I repeated Example I and formed clear microemulsions spontaneously attemperatures ranging between 30°-70° C. by merely combining in acontainer, 50 parts of de-ionized water, 50 parts ofhexamethyldisiloxane (MM), and 42.9 parts of silicone polyether. Theoptical clarity was the same as obtained in Example I.

EXAMPLE XII

I repeated Example XI and formed clear microemulsions spontaneously attemperatures ranging between 43°-56° C. by merely combining in acontainer, 50 parts of de-ionized water, 50 parts ofhexamethyldisiloxane (MM), and 17.7 parts of silicone polyether. Theoptical clarity was the same as obtained in Example I.

Table I provides a summary of Examples I-XII. In Table I, Ratio 1 is theamount of oil divided by the amounts of oil and water. Ratio 2 is theamount of surfactant divided by the amounts of oil, water, andsurfactant. Percent Surfactant is obtained from the relationship (Ratio2) divided by (1-Ratio 2)×100.

                  TABLE I                                                         ______________________________________                                                 Temperature                                                          Example  (°C.)                                                                              Ratio 1 Ratio 2 % Surfactant                             ______________________________________                                        I        47-62       0.5     0.2     25.0                                     II       60-68       0.5     0.2     25.0                                     III      44-60       0.4     0.15    17.6                                     IV       20-30       0.5     0.15    17.6                                     V        22-41       0.7     0.2     25.0                                     VI       30-85       0.5     0.4     66.7                                     VII      42-58       0.5     0.2     25.0                                     VIII       36-69.6   0.5     0.22    28.2                                     IX       30-46       0.5     0.18    22.0                                     X        20-25       0.5     0.22    28.2                                     XI       30-70       0.5     0.3     42.9                                     XII      43-56       0.5     0.15    17.6                                     ______________________________________                                    

As can be seen in Table I, compositions according to my invention can beprepared at temperatures generally in the range of 20°-85° C. Theycontain 5-70% by weight of surfactant, most preferably, about 15-30% byweight of the surfactant; with the balance being oil and water. Theproportions of oil and water generally fall between 40:60 to 80:20, or0.4 to 0.8 as defined above for Ratio 1.

EXAMPLE XIII

I formed a number of optically clear microemulsions spontaneously atroom temperature (22° C.). In this example, compositions representativeof my invention were prepared, wherein the mixing ratio of the threecomponents comprising water, oil, and surfactant, was within the shadedarea in FIGURE 1 of the drawing, i.e. the area surrounded by the linesconnecting points A, B, C, D, and E. I formed these microemulsions inthe same manner as in Example I. Thus, I merely added the threeingredients to a container. No mixing, stirring, shearing, or input ofmechanical energy for agitating the three ingredients was required. Thepolyether corresponded to the same compound used in Example I. I wasagain able to read text through a two centimeter diameter bottle filledwith these microemulsions. They contained particles having an averagediameter of less than 100 nanometers (0.1 microns).

EXAMPLE XIV--COMPARISON

I repeated Example I and formed a number of emulsions at roomtemperature. However, in this COMPARISON EXAMPLE, I used a silicone oilequivalent to the silicone oils described in Bailey's U.S. Pat. No.3,299,112. Thus, Bailey's silicone oil is said to correspond to R"₃SiO(R"₂ SiO)_(x) SiR"₃ with x being 10-1,000. I followed the teaching inBailey, but was not able to read text through a two centimeter diameterbottle filled with these Bailey emulsions. As noted in the BACKGROUND OFTHE INVENTION, my invention in one embodiment involves using a volatilelinear VMS having an "x" of 0-5, well below the range in Bailey. In thisCOMPARISON EXAMPLE, I verified that where "x" exceeds 5, thecompositions are not clear.

Other variations may be made in the compounds, compositions, or methodsdescribed, without departing from the essentials of my invention, theforms of which are exemplary, and not limitations on its scope asdefined in the claims.

I claim:
 1. A method comprising spontaneously forming a microemulsionwithout mixing, stirring, shearing, or input of mechanical energy foragitating ingredients used to make a microemulsion, by simply combining(i) water; (ii) a cyclic methyl siloxane having the formula {(CH₃)₂SiO}_(p) or a linear methyl siloxane having the formula (CH₃)₃SiO{(CH₃)₂ SiO}_(q) Si(CH₃)₃ in which p is 3-6 and q is 0-5; and (iii) asilicone polyether having a formula selected from the group consistingof ##STR8## where R1 represents an alkyl group containing 1-6 carbonatoms; R2 represents the radical --(CH₂)_(a) O(C₂ H₄ O)_(b) (C₃ H₆O)_(c) R3; x has a value of 0-3; y has a value of 1-3; z has a value of0-2; m has a value of 3-5; n is one; a has a value of 3-6; b has a valueof 4-20; c has a value of 0-5; and R3 is hydrogen, a methyl radical, oran acyl radical.
 2. A method according to claim 1 in which the methylsiloxane is present in the microemulsion in the form of droplets havingan average diameter of less than 100 nanometers.
 3. A method accordingto claim 1 in which the methyl siloxane is octamethylcyclotetrasiloxane.4. A method according to claim 1 in which the methyl siloxane isdecamethylcyclopentasiloxane.
 5. A microemulsion prepared according tothe method defined in claim
 1. 6. A microemulsion prepared according tothe method defined in claim 3, the microemulsion having a compositiondefined by and within the shaded area depicted in the annexed soleFIGURE 1.